Colon Cancer Tumors and Disease Recurrence Differ by Race

Many colon cancer disparities found in patients of different races under 50-years old.

According to a recent study from the Mayo Clinic Cancer Center, the genetic makeup of colon cancer tumors and survival rates for patients differ by race.

“These findings put the issue of race more prominently on the radar of investigators that cancer biology may contribute to race-based disparities,” said study co-lead author, Harry Yoon, MD, an oncologist at Mayo Clinic. “While it is too early to change the way we treat these patients, our results indicate that future studies are needed to examine potential biological drivers of these differences more closely.”

Colon cancer is the third most common cancer in both men and women, according to the American Cancer Society, and more than 93,000 cases are estimated to be diagnosed in 2015.

Scientists have long been aware of the fact that blacks develop colon cancer at an earlier age and that blacks with colon cancer are at higher risk of dying from their disease than are whites. However, it has been difficult to properly identify the causation of these disparities.

To shed light on this issue, researchers analyzed data from a large clinical trial of more than 3000 patients with stage 3 colon cancer. The analysis revealed that blacks, whites, and Asians had differences in the frequencies of mutations in 2 cancer-related genes, BRAF and KRAS, both of which are associated with worse outcomes for patients.

The analysis also showed that blacks were twice as likely to have recurrence of their disease than whites, but this was only true in those patients aged under 50 years.

Potential contributing factors to this disparity include socio-economic factors, such as diagnosis at a later stage, decreased access to health care, and suboptimal treatment.

“The role of the biology of colon tumors according to race has not bene examined as extensively,” Dr. Yoon said. “This biology can be reflected in the genetic makeup of tumors, as well as by whether and how quickly cancer returns after the patient has been treated.”

The researchers focused on finding out if colon cancer is genetically different based on race. In addition, they focused on whether race-based differences exist in recurrence rates.

The researchers examined data from the Alliance N0147 trial, which included patients with stage 3 colon cancer who underwent surgery to remove the cancer and had subsequent chemotherapy.

Patients self-identified as either black, African-American, white or Asian as a part of the trial. Then each patient’s tumor was evaluated to see if a mutation was present in the cancer-related genes BRAF and KRAS.

Recurrence rates were also recorded. The data showed that tumors from whites, black, and Asian patients were different in terms of the frequency of mutations in the BRAF and KRAS genes.

Whites were found to be twice as likely to have mutations in the BRAF genes, while blacks had the highest frequency of KRAS mutations. However, Asians were most likely to have normal copies of both genes.

According to the analysis, blacks had more than double the risk of cancer recurrence compared with whites, but again, this disparity only held true for patients under the age of 50 years. Nearly half of younger black patients experienced recurrence within 5 years of treatment, compared with only 22 to 35% of white or Asian patient populations of any age.

This difference could not be explained by the genetic mutations most frequently found in the tumors of the different races.

“Because all patients were treated and had their disease monitored in a clinical trial, suboptimal treatment, differences in cancer stage, or reduced access to care cannot adequately explain the disparity,” Dr. Yoon said.

The researchers adjusted the data for a number of potential confounding factors such as tumor grade, the degree of lymph node involvement, depth of tumor invasion, body mass index, location of the tumor within the colon, history of smoking, and anomalies in mismatch repair genes.

However, none of these factors seemed to have an effect on the outcomes for young black patients.

“In addition to published data indicating that a limited number of genes are preferentially mutated in colon cancers from black versus white patients, our study revealed differences in the mutation frequencies of BRAF and KRAS oncogenes that provide prognostic information in colon cancer patients,” said Frank Sinicrope, MD an oncologist at Mayo Clinic and co-lead author. “Our data provide further evidence that colon cancers from blacks are intrinsically different and are associated with more aggressive clinical behavior in young black patients.”